1. Field of the Invention
The present invention relates to a method of producing a semiconductor thin film and, more particularly, to a method of peeling a semiconductor thin film and a method of producing a solar cell using the semiconductor thin film.
2. Related Background Art
There is the known technology of forming a semiconductor thin film through a peeling layer such as a porous layer or the like on a semiconductor substrate and thereafter peeling the semiconductor thin film away from the semiconductor substrate. Specific peeling methods include methods by etching and mechanical peeling methods with application of external force.
As an example of the latter, Japanese Patent Application Laid-Open No. 7-302889 (CANON K.K.) describes the technique of forming a porous layer on a surface of a first silicon wafer, thereafter forming an epitaxial silicon layer thereon, bonding a second silicon wafer to the epitaxial silicon layer, further bonding plates to the respective silicon wafers, and then separating the plates from each other, thereby peeling the epitaxial silicon layer away from the first silicon wafer.
Japanese Patent Application Laid-Open No. 8-213645 (SONY CORP.) describes the technology, similar to the above, of forming a porous layer on a surface of a single-crystal silicon substrate, thereafter epitaxially growing a pn junction (solar cell layers) thereon, bonding the back surface of the single-crystal silicon substrate to a jig with an adhesive on one hand, and also bonding another jig, for example, of metal, quartz, or the like to the side of the solar cell layers to be peeled off on the other hand, and thereafter separating the two jigs from each other, thereby peeling the solar cell layers away from the silicon substrate.
In the peeling of the semiconductor thin film or the solar cell layers according to the conventional techniques, each of the silicon substrate side and the side of the semiconductor thin film to be peeled off is supported by the rigid body or by the flat plate with low flexibility and thus the flat plates bonded are separated away from each other on the occasion of peeling. Therefore, considerable force is necessary for the peeling. This could result in damaging the semiconductor thin film expected to be utilized. In addition, the above techniques require a step of applying and curing the adhesive for securing the substrate to the plate or to the jig, which is the cause of decreasing productivity. Further, the adhesive remains on the back surface of the substrate and the above techniques thus necessitate a step of removing the adhesive in order to recycle the left substrate.
An object of the present invention is, therefore, to provide a peeling method for peeling the semiconductor thin film away from the substrate without damage in an easy way.
Another object of the present invention is to provide a method for holding the substrate without contamination.
The present invention provides a method of producing a semiconductor thin film comprising the step of rotating a support member having a curved surface while supporting a semiconductor thin film formed on a substrate, on the curved surface of the support member, thereby peeling the semiconductor thin film away from the substrate. According to this method, the semiconductor thin film can be peeled off the substrate in an easy way. At this time, it is preferable to increase the radius of curvature of the curved surface with progress of the peeling. The present invention also provides a method of producing a semiconductor thin film comprising the step of peeling a semiconductor thin film formed on a substrate away from the substrate, wherein magnitude of an external force for peeling the semiconductor thin film decreases with progress of the peeling.
Further, the present invention provides a method of producing a semiconductor thin film comprising the step of peeling a semiconductor thin film formed on a substrate away from the substrate, wherein the step of peeling is carried out after the substrate is secured on a substrate support member without an adhesive. According to this method, the substrate can be secured without contamination. The substrate is preferably held by vacuum suction, by electrostatic suction (adhesion), or by a securing claw.
The present invention also provides a method of producing a solar cell comprising the step of forming a separation layer on a substrate and forming a semiconductor thin film having a semiconductor layer of a first conductivity type and a semiconductor layer of a second conductivity type on the separation layer, the step of bonding a light-transmitting film onto the semiconductor thin film with a light-transmitting adhesive, the step of exerting an external force on the light-transmitting film to peel the semiconductor thin film away from the substrate, and the step of forming an electrode on a back surface of the semiconductor thin film thus peeled. Further, the present invention provides a method of producing a solar cell comprising the step of forming a separation layer on a substrate and forming a semiconductor thin film of a first conductivity type on the separation layer, the step of bonding a light-transmitting film onto the semiconductor thin film of the first conductivity type with a light-transmitting adhesive, the step of exerting an external force on the light-transmitting film to peel the semiconductor thin film of the first conductivity type away from the substrate, the step of forming a semiconductor thin film of a second conductivity type on a back surface of the first semiconductor thin film thus peeled, and the step of forming an electrode on the semiconductor thin film of the second conductivity type. According to the above methods, the solar cell can be produced through the simple steps.